<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>


    <div></div>

    <script>
        
        console.log(window.document);

        console.log(document.documentElement);   // html

        console.log(document.head);

        console.log(document.body);

        console.log(document.title);    // 可读可写

        setTimeout(function() {
            document.title = '我变了'
            // document.body = 'hello world'
        } , 2000)


        // console.log(document.body.div);   // 错误的

    </script>
    
</body>
</html>